Tickets - Athletic Club

I have a illusion of at least per one time watch a match of athletic club on San Mames. However i want to know what is the best way to buy tickets.

I checked in the last months the "Tienda Athletic" however, for all the time, or the lowest price tickets have only 1 seat (need 2) or are already at a expensive price 90€/120€.

I'm doing the comparasation with FCPorto, where the tickets are around 20€/60€, for all the games.

Will be possilble to receive some lights about this?

Thanks for all